Single sheet loss tester



s. c. LEONARD ET Ax. 2,861,241

SINGLE SHEET Loss 'TESTER Nov. 18, 1958 4 Sheets--Shee'rl 1 Filed Ap-,ril 29, 1955 lul s. c. LEONARD ET Ax. 2,861,241

SINGLE SHEET Loss TESTER Nov. 18, 1958 4 Sheets-Sheet 2 Filed April 29, 1955 Imke@ wmf E WEER/ mwmf Ene fil/vf' Nov. 18, 1958 Filed April 29,

s. c. LEONARD SINGLE: SHEET Loss 4 Sheets-Sheet 3 v f C. VLTHE REFERENCE 50U/iCE MPL/HER l I r75g? .//6 I I zw y 1 l I/2 I 1 i` l i Il @gua/mmv f l V rv I I l IL l AR Pani/f r.//9

/ffcr/F/m mlm/Hm .:750 Alva 0.a.. -Q L )45 #faul/non j; n. c. afl/va vou/vae l m55 /w Heal/man j mm? /6 /z/ .EL 34 33 20/ 20 l j I ,i 15am/vcr DETEC TOR/7 s. c. LEONARD ETAL SINGLE SHEET' Loss TESTER N0v.18,195s

v.United States flosses in strips of magnetic vmaterials.

lil

A`snsrGiL-E snaar Loss TESTER Stephen C. Leonard, Cheshire, `Robert L. Ten Broeck,

Plttsield, and Lewis' R. Runaldue, Dalton, Mass., as-I ;signorsto General Electric Company,ua ,corporation of New York VApplicationApril-29,V 1955,'Serial No. 50g-1,722

v 13 Claims. (Cl. 324-34) kThis invention; relates to :the determinationA of t characteristics of magnetic materials,A and more in particular to an improved methodand apparatus for measuring the While the invention hereinafter disclosed is perhaps of greatest in- :ft'erest in theidetermination-v-of losses of single laminations of. transformer cores, it will-be obviousy that the scope'of-the invention is not so limited.

Previous tests for determining the losses in transformer .core laminationsV may be arbitrarily separated into three groups, the first group involvingfthe determination fof the* losses in an -assembled core, the second test involving the determination of lossesfin-samples Vcut .from single laminations, and -the third testproviding an indication of the losses ina -single lamination strip prior to assembly of the core. In the past it has been common to apply onlyzthe'rst and second abo-ve stated tests, since equipment available for testing single com- 'plete laminations necessitated a considerable,expenditure of time to adjust and was therefore` not practical to employ from the production standpoint. The secondj'test e.,-test1nglof samples cut from ysingleulaminations) -obvlously resulted in the destruction of vthe lamination from which the sample was cut, and also necessitated the `:annealing of the sample in order to relieve cutting stresses. While the testing of samplesrisusefrul inde.-

1-ftermining'the basic qualities of'the lamination material,

it has been found that no accurate correlation exists between the results of this test and the results of the -ftest on the assembled core. Therefore in order to predict the characteristics of artransformer core priortoas- :sembly it isimperative to obtain a'testingmethod*l that permits the determination Vofthe quality of magnetic material in its simple lamination condition.

. It is therefore an object of thislinvention to provide #an improved method andappar'atusftor determining the -loss characteristics ,ofV strips of magnetic material.

Another'object is to provide a' non-destructive method and apparatus for Areducing the time required to measure the loss characteristics of ,strips of magnetic material.

Still another object Yof this invention is to provide an improved apparatus for determiningthe loss'tcharacter- "istics of strips of magnetic material requiring aminimum of adjustments and being. readily adaptable to automatic vg-operation.

A further object of this invention is .toprovideauondestructive testing device for automatically measuringV Y'the loss quality oflaminations ofV magnetic material at :a predetermined flux densityand indicating the loss measured directly in watts per pound.

Briefly stated,..in accordance With'one'laspectotrthis invention, .we lprovide a test jig having a rnagnetizing coil and a"B coil surrounding a lamination to betested,

andan H coildislposed oneach side o f the lamination. AThe magn'etizingcoiLis suppliedfwithna currentlprovidingfluX in th'elarninatiom A voltage induced infthefB coil cont'rols a'feedbaclc arrangementto maintain a con- -starrt ilux'density in thelarnination, and a portionof 2,861,241 timeined4 Nov. 18, 195e lthe ,B,vol tage ismalso; appliedto, one coil-of aw'attl` meter. Theyolta'geoutput of the H coilzis appliedY by vWay of an integrating. amplifierghaving essentiallyfran infinite` j impedance, input tothe other coil `of.A the watt-v meten A computer circuit lis .provided in,order that, tl1e yWattmeter read directly .in Ytermswof Watts perpoundof lamination, and that `thelonly information required to be, manually; SetonV tlief deviceV are ythe Weight, width,- and .length 'ofthe 11.2l'rn1i-nafiQfl.-brina tested Theinventionwill be. better understood A.from the ,fol-

. lowing ,descriptionmtalgen inconnection withrthevaccome panying drawings,"and its 's cope,..wi1l be pointed` out iii the appended claims.

In thedraw'ings,

Fig. 1, isv apartiahblock VA c'liagramillustrating .one rem- `bodiment of thevsinglsheet loss tester ofthis invention,

lFig. 5 2 is y a. partially ldcross:sectional perspectiveg view Y of the elementsof the testfjig employed with'thisinve'ntion, v

v Fig. 3(a) andv y3 (b) 'isa ycircuit'diagramvof a typical single sheet -lossi testerv designed according to this invention, Fig. 3(b) being ahorizontal extension `from the .right hand side of Fig. 3,(z), and

Fig. 4 .is an lexaggerated vector diagram ofthezyoltages in ,the integrating circuit` of Fig., 3.

Referringnowrtoptheg'block diagram (Eig. 1),;acore lamination 10 to ybeltested yis, inserted in a margnetizing adjacentftothe lamination; 10, theragrisvof the fHl, coil ,being lpartdlel yto the axisA ot the masnetizing, Coilfand 'B" coil. "TheV magnetizingcoil,, fB coil and Hcoil compriseA av ,test jig. Magnetizing ,current for inducing a'. flux' Yin .the` la .natiorlgis sppplied to the, ,.magtletliilg c oil A11V from ,ur'ce of 'alternating current 14, A sueltas a. 115 v01ti60 Cycle ,Surplyrbywawt an. alternatingiirlrentregulatorl'llS `V`to; maintain, a constant. inputf source for the` magnetiging "coil,l al step" down l transformerk 1.6,V a

voltageand thus produpce'lasgnearly l*as possible/asincwave `voltage a. pQtentiQmeter. 18,121.1@21 .power ample Iier-19. gflfhej. output `,voltage ofthe poyverzampli'tierlis' parallel ,resistive circuithaving one leg comprisedmof `a .series 'combination of thicknessl rheostat, zztala watts adjustment potentiometer 24and ,volt'sfa'djustment potentiometer 25. The otherleg consists'of. a

mechanically` coupled ',togetherj andare so proportioned ythat lvariation thereof,produces` no change in the overall resistance of the parallelV :circuitA frompoint fXfwto point Y. That is, ,anirlcreaseor` decrease of resistance of rheostatwZZ (n) vaccompanied'by? a decrease `or increase respectively of resistance of frheostat 'l22(b) (by virfuetofth mechancralnnuplng betweenthatwo rheostats) ofl'such a,magnitude that thezresistanceI of the ,parallel circuit' of rheostatg 22(01) in,.,se ,ries d with potentiometers ,24,l and 25;, and rheostat. }22(b) in` :series with Vresistor'Zra remains 5constant,- and `thereforewhe ,resistance between points Xf and fY remains constant.

' ThusY a .variation of the j "fthickness?1 adjustment doessnot `vary the" eectof the fwitfhg adjustment., 'circuit resistance aan begch'osen .t0 ,limit the] j Widtlrsheet"thatl the computer'can handle.

The-.Parallel inimum @Thegarmcf the voltsf potentiometer 25k isjconnected to a rectifier circuit and-stabler amplifier circuit 26, 'and the arm of i t 3 the watts potentiometer 24 is connected to the B amplifier circuit 27. The computer circuit 20 is connected to the B coil. It is preferred that the rectifier circuit be of the averaging type.

The voltage appearing at the output leads 29 and 30 of the rectifier and amplifier circuit 26 is a unidirectional voltage proportional to the average of the alternating current voltage of the B coil 12. This output voltage (on leads 29 andV 30) is connected in series opposition with the output voltage of a direct current voltage reference circuit 31, and the combined signal is applied to the input of a conventional servo amplifier 32. The

output of the servo amplifier 32 is connected by conventional means to a servo motor 33, which is mechanically i coupled to thearm 34 of potentiometer 18. -The circuit comprised of the B coil, the computer, the rectifier and stable amplifier, the direct current voltage reference I circuit, the servo amplifier and motor, and the potentiometer 18 serve to automatically maintain the fiux density in the lamination at a constant value. This value is Y dependent upon the setting of the width and thickriess adjustments of computer 20. These adjustments may be rapidly made, and the circuits are comprised of commercially available components.

As previouslyV stated, the arm of the watts adjustment potentiometer 24 of computer circuit 20 is applied to the B amplifier 27. The B amplifier is a stable alternating current amplifier having no appreciable phase shift. The output of the B amplifier is applied to one winding of a light-beam wattmeter` 40.

The voltage induced in the H coil 13 is proportional to the finx in the field adjacent to the lamination and is therefore proportional to the time derivative of the magnetomotive force adjacent to the lamination 10 being tested, since the core of this coil, as will be described in more detail later, is of non-magnetic material. The H coil voltage represents the mathematical derivative of that part of the current in the magnetizing coil necessary to magnetize the lamination directly under the H coil. The voltage of the H coil is applied to an electronic integrating circuit 41, andY by way Yof an H amplifier 42 to the light-beam wattmeter 40. The

y H amplifier 42 is similar to the B amplifier 27. VBy integrating the H voltage, a voltage is obtained that is proportional to the current required to renergize that Y portion of the lamination covered only by the area of the H coils. Y

The basic construction of a suitable test jig is illustrated in Fig. 2. Therein the core laminationV 10 to be tested is shown extending throughthe magnetizing coil 11 and the B coil 12, with the longitudinal-dimension of the lamination being parallel to the axis of the magnetizing coil and the B coil. The B coil is positionedl inside of the magnetizing coil. An H coil 13 is positioned adjacent the top side of the lamination and inside of the B coil. A similar H coil 13a is also positioned adjacent the bottom side of the lamination and inside of the B coil. The axis of each H coil Vis parallel to the axis of the B coil. The turns of the Hk coils do not encircle the lamination, but instead are wound on a non-magnetic formand are positioned as close to the lamination as possible. The magnetizing coil 11 Yis longer than the B coil, and extends beyond thev ends of the B coil.r As previously stated, the voltage induced in the B'coil is proportional to the fiux induced in the lamination 10. Therefore, it is desirable that the -B" coil be located as close as possible to the lamination. Since the terminals of the B coil are connected -across a resistance network in the computer circuit, a current fiows Vthrough the B coil, and this Y current may affect to some extent the 'magnetizing forces Y producing the ux in the lamination. Therefore, in order i toY determine more accurately the magnetomotiveV force l dropV in the lamination, it is desirableihat the H coils be located inside of the B coil. The magnetizing c oil 11 is made as long as possible in order that the ux linking the B and H coils be uniform. A magnetic return path (not illustrated) may be provided surrounding either all or part of the outside of the coils in order to increase the uniformity of the fields of the coils. In a modification of this arrangement, the B" coil may be located inside of the H coil, however, this modification is preferred only if no current passes through the B coil.

Theory of operation in which the magnetic field is uniform and parallel to the axis of the core is:

leg-f4 eid: 1)

where f is the frequency in cycles per second, n is the turns per centimeter of length of the magnetizing coil, N is the number of turns in a uniform secondary winding, such as the B coil surrounding the core, A is the cross sectional area of the core in square centimeters, e is the voltage induced in the secondary winding, and i is the theoretical magnetizing current in the magnetizing winding assuming ideal circuit conditions.

The Voltage eH induced in a coil, such as the H coil, located in the field adjacent the sheet will be equal to:

do dB where Nfl is the number of turns on the H coil, is

the total linx in the H coil, AH is the cross sectional area of the H coil, and B is the fiux density in the H coil. Since the permeability `of the medium enclosed by the H coil is unity,

dHs

where HS is the kmagnetomotive force drop in the sheet. Solving for Hs:

Since the magnetomotive force is proportional to the product of the current i and the turns n of the magnetizing coil,

Thus integration of the voltage en provides a current that represents the current i, and that current is xapplied to the wattmeter coil.Y The detiection -of the wattmeter is proportional to the integral of the .current applied to its coils, the average power per unit weight indicated by the wattmeter being:

Wj-EOIO GOS d1 where p is the phase angle between the effective output voltage E0 of the B amplifier and the effective output current of the H amplifier, and d is the density of the l sheet.

In order to automatically compensate for the variation I of the area A in Equation 7 so that the wattmeter 40 indicates watts per pound directly, thecomputer 20 is connected between the output of the B coil and the input of-.the B amplien27. .Thev-actionqof thejwcomputerfis i ysuch that, -whenl af'se'ttingds -frnade on ithefwiglth` ,fr-heostat 21,.thickness rheostat 22a and thecornpensator frheostat 22b that is related to the lwidth andrthickne'ss .of'theflarni- .nation 10, the-servo controlled voltage supply forthe magnetizing coil 11' establishes a predetermined'flux density Bm in the lamination. The flux densityfBmzinlthe. lamination is equal to:

KSEB

"where K3 isconstant for a given1frequency ofrxcitation and is inversely proportional to the number bf-turns-of the B coil, EB is the lvoltage o'utp'utoffthe '-fB cil,

andA isthe cross-sectional area 'of 'theflamination 10 under test. j, v

' Since the outputfvoltageof the rectifier and-'amplifier 26 is compared with a reference voltage,vtheiservo "mechanism tends to maintain a -constant voltage input its);

to the rectifier,y and thus Amaintains av constantvoltage onv 'Ithe arm of thel volts adjustment potentiometer"25 l-r'egardless ofthe ysetting of the width and thickness `rheostats. In order to rmaintainlthis'voltagev constant, the outputvoltage ofthe power amplifier 19 may- Varyythus varying the 'imagnetor-rrotiveV force o-fthe magnetizingl 'coil,. and'the output .voltage ofthe B coil. By/proper selection of the resistance values inrthe `computer circuit, variations of the output voltage ofthe power amplifier 19 are such that a constant predetermined Value of ux density is maintained in the lamination V10,and`this predetermined value is.dependent-upon`the setting -of the -volts adjustment potentiometer 25. T-he resistance values in the computer circuit are-selected'such -that in order t0 maintain aconstanttlux density in various Vsizedflamirrations it is only=necessary to adjust fthefvalues ofr the width andlthickness rheo-stats. vvThe parallel '-arrn ofthe computer 20 consisting ofresistor 23 and thickness cornpensator 22b-servesto maintain a constantresistance value between ground and the vbottom-'of the-widtlirheostat (at'lpoint I x)V regardless of 'the-setting of the ganged rheostats 22a and 22bs0- that the width "and thick- ---ness settings are independent of each other.

EFIQB.. c)

' laminator, or:

-the watts adjustment potentiometer 24, and thefoutput voltage E01 of the B amplifier is:

"where aB is' the amplilication factor ofthe B amplilier. Solving for the-areaA in Equation. 8 and substituting Bm from Equation 10 gives:

KaE'asKr E01 i Then' from Equations 7, 8 and 11,

W- dK3K4 "Thus" vby..employing the computer `circuitl .and "the .servomechanism tomaint'ain a constant flux densityln the lamination and a constant voltageinput to the ..B

watts amplifier proportional to the ux density, the wattteter t5" ferent densities.

'Typical circuit Referring now to the circuit diagram-of `Figs. 3a land 3b, infFig. 3a the input of' alternating current voltage regulator ll5is shown connected to 60 cycle alternating current supply 4lines' 50. Thev output of the regulator v15 is connectedv to the-primary winding of step down translformer 16, and yalso to a conventional rectitier and'dii'ectcurre'nt regulator circuit 51. The rectifierv and di- -rect current regulator-51 may be used to supply a stable voltage' for various circuits of the loss tester. The secondary-winding'of step down transformer is connected to the band pass filter 17. The band pass lter is tuned -to 160C. P. S., and serves to remove the harmonic cornponents-ofthe -voltage so that the output voltage applied topotentiometer 518-is as nearly a sine wave as possible. The/arm 34 of potentiometerl is connected-to theA input of poweramplifierl 19, and the output of the power amplilier is connectedbyway of the center arm of switch 52a vof a ganged test-calibrate switch 52y (shown in test position) to thel magnetizing coil 11.

The -B coil 12 of the test jig is connected by way -Iof switch 521; of1testcalibrate switch 52 to one end of "width adjustment rheostate 21 in the flux density computer circuit (Fig. 3b), (which serves' the same function as the computer circuit 20 of Figure l). vThe -other end ofthe width adjustment rheostat 54 is connected byl way of switch 56e of range switch 56 to a resistance '57, wihch is in turn connected toyone lend of eachf-of the. ganged thickness adjustment rheostat fshown in VFig.v 3b)y the circuit values of the loss tester 'ofthis'linvention may be selected to test laminations having" thicknesses of 14 mils plus or minus 10% while the other range may have circuit values to test laminationshaving thicknesses of l2 mils plusv or minus 310%.

-When the range switch is in the position shown in Fig. db, the bottom end ofv thickness rheostat 22a `is connected to groundby way ofresistor 61,` watts adjustment potentiometer 24, volts adjustment potentiometer 25, and resistor'Y 64, while in the other range'the i"bottom end of the thickness potentiometer 22a is clonnected to ground by way of watts adjustmentpotentiometer65,-resistor` 66, volts adjustment potentiometer 67 and resistor 68. Similarly, when the range switch jis'in'theposition illustratedy in Fig. Sb'the bottom endfof jcompensator '22b `is grounded by way of resistor 23, while lin the "other range the compensator 22b''is `jgroui1diedby lway of resistor '70. Av pair 'of terminals [.71j'are provided' betweentheitop end of Width rheostat 721 forcalibration"purposes asl will "be described later.

i 'lheivalnes of" l'resistorsv andv potentiometers areyso adjusted that for" a"given"range," when the `resista-,nce"of upon the operating range) is connected by way of range switch section 56a to van alternating current amplifier having voltage feedback through a rectifier. The output of the rectifier in this unit is proportional to the `average of the input voltage. This type of circuit is employed since the voltage input may not be a pure sine Wave. The output voltage of the rectifier is connected in series opposition with a direct current voltage reference source 75, and the difference voltage is thenr applied to the input of a conventional servo amplifier 32. The direct` current voltage reference may be of any type producing a stable output voltage, such as a battery or the conventional reference source illustrated in Fig. 3a. As illus- Hated, the reference source is comprised of a full wave rectifier circuit consisting of transformer 76 and rectifier tube 77, a filter capacitor 78, two stages of regulation v consisting of resistances 79 and 80 and voltage regulating tubes 81 and 82, and voltage dividing resistances 83 and 84, the output voltage appearing across resistor 84. The output voltage from the servo amplifier 32 is connected to servo motor 33 by way of the normally open contacts 86 of relay 87. The relay 87 is energized from a source of voltage at terminals 88 when the manual operate switch 89 is closed. Thus the servo motorwill turn only when the operate switch 89 is closed. The servo motor drives the arm 34 of potentiometer 18.

The circuit as disclosed thus far provides automatic means for maintaining a constant flux density in the lamination when the width and manual thickness rheostats are set to values corresponding to the width and thickness of the lamination. The magnitude of this flux is determined by the setting of the volts adjustment potentiometers and 67.

The voltage appearing on the arm of watts adjustment potentiometer 24-(or on the arm of watts adjustment potentiometer depending on the setting of the range switch section 56h), is applied to the input of the B amplifier 27. The B amplifier is an alternating current amplifier having negligible phase shift and a predetermined transconductance. vAlthough other circuits satisfying these conditions may be employed, the

. circuit illustrated in Fig. 3b has been found to be very satisfactory. The first stage of this amplifier is com.

prised of an input capacitor 100, a first amplifier tube 101, control grid resistor 102, a plate dropping resistor 103, and filter capacitor 104, a plate load resistor 105, a' screen dropping resistor 106, and screen by-pass capacitor-107, a fixed bias resistor 108, a coarse bias adjustment rheostat 1,09 and a fine bias adjustment rheostat in series with resistor 111. The second amplifier stage is comprised of `an input capacitor coupling the plate of the first amplifier tube 101 tothe control grid of second amplifier tube 116, input voltage dividing resistors 117 and 118, a capacitor 119 connected between the control grid and ground to eliminate spurious oscillations, a platevdropping resistor 120 and by-pass capacitor 121, a plate load resistor 122, a screen dropping resistor 123 and screen by-pass capacitor 124,

. a fixed bias resistor 125 and a bias rheostat 126. v The plate of the second amplifier tube 116 is coupled directly to the control grid of a cathode follower tube V having a bias resistor 131. A capacitor 132 connected between the control grid of the cathode follower and ground'prei vents spurious oscillations. The output of the amplifier is connected from the cathode of the cathode follower by way of a coupling capacitor 133 and resistor 134 to one coil 135 of the light-beam wattmeter 40. In order to reduce phase shift in the amplifier a feedback is provided by means of lead 136 between the output Vand the cathode circuit of the first amplifier tube 101. A

`eliminating spurious oscillations.

, 8 capacitor 137 across the wattmeter coil 135 aids in The second stage of the amplifier is directly coupled to the cathode follower in order to eliminate one phase shift introducing coupling network. Typical values for the components of the B amplifierv may be as follows: Tubes 101 and 116 are 6BH6s, tube 130 is a 6L6, resistors 102 and 105 are 500,000 ohms, resistors 103 and 122 are 100,000 ohms, capacitors 104, 107, 121, and 124 are 20 mfd., resistor 106 is 2.2 megohms; resistor 108 is 4000 ohms, rheostat 109 is 500 ohms, rheostat 110 and resistor 111 are 10,000 ohms, capacitor 115 is 0.01 mfd., resistor 117 is 290,000 ohms,.resistor 118 is 600,000 ohms, capacitor 119 is 0.0015 mfd., resistor 120 is 50,000 ohms, resistor 123 is 300,000 ohms, resistor 125 Ais 2000 ohms, rheostat 126 is 1000 ohms, resistor 131 is 5000 ohms, capacitor 132 is .001 mfd., resistor 134 is 5000 ohms i and capacitor 137 is 0.005 mfd.

The electronic integrator The electronic integrator 41 (Fig. 3b) is comprised of a cathode follower stage having a phase shifting net- ,work, and two amplifying stages. The cathode follower stage has an input capacitor connected to the con- Htrol grid of cathode follower `tube 15,1, a grid resistor 152 having one end connected to the control grid of the tube Y151 and the other end connected to the junction of series ,cathode resistors 153 and 154. The plate of the tube ,A is connected to a source of direct current potential by way of plate dropping resistor 155, and'by-pass capacitor 156 is connected-between the plate of the tube 151 and ground. A coupling capacitor 157 couples the cathode of tube 15,1 to a point 158 on an integrating network comprised of a first resistor 160 in series with a first capacitor 161, the series combination being in parallel with a series circuit comprised of rheostat 162, second resistor 163 and second capacitor 164, and a third resistor' 165 is connected between the junctions of the first resistor 160 and first capacitor 161 and the second resistor 163 and second capacitor 164. This integrating network is the subject of copending application Serial No. 588,-

, V925, filed June l, 1956, now Patent No. 2,846,643, of A. H. Foley and assigned to the present assignee. The

output from the integrating network from the junction of first resistor 160 and first capacitor 161 is connected to the control grid of a first amplifier tube 1 70. A resistor i 171 in parallel with the integrating network serves as a grid resistor for the tube 170. The first amplifier stage is comprised of a plate load resistor 172, a screen dropping resistor 173 and by-pass capacitor 174, a fixed bias resistor- 175, anda gain control bias potentiometer 176.

.The output-of theiirst amplifier stage is coupled by 'means of capacitor 177 to the control grid of second amplifier tube 178. The second amplifier stage is comprised of plate load resistor 179, screen dropping resistor and screen by-pass capacitor 181, cathode bias resistor 182 and by-pass capacitor 183, a feedback from the plate of tube 178 to the cathode of tube 170 cornprised of capacitor 184 and resistor 185, and in control grid resistor 186. The feedback reduces overall phase shift in the amplifier stages, so that the amplifier has only a negligible amount of phase shift. The plate load ,resistors of the two amplifier stages may be Vconnected by way of resistor 187 to a source of direct current potential, and the supply voltage may be filtered by a capacitor asomar Referring,.now .tEiV-g. 4, thereinis-...illustrated anexaggerated vectordiagram of...the-.vltages. roftheintegrat- .ing-network .comprised of.resistors.160, 1163, and :165, :potentiometer 162, .and :capacitors ..161 and 164. The vector Em represents the voltage appliedtothe lintegrating network between point-158 and-ground. The ratio `ofresistance of rst resistor 160 vto the reactance of lrstcapacitor l161 isipreferably about 20:1, while the .ratio of resistance of second resistor..163 and potentiometer `162 .to the reactance ofsecond capacitor 164 is somewhat less, Ybeing about 10:1. Therefore, the angle between the-vector 'Ergtrepresenting the voltage across `resistance 163 `and:rheostat.;162) and the .vector .Em is Vgreater than the rangle between ythe vector iErl -(repre senting the voltage .across resistor .1160) `and the vector fEm, andthevector Ec2 (representing ythe voltage across v.capacitor .164) zis Y greater ,than lthe vectorEcl (representlingfthe voltage across -capacitor 161'). ':Since the re- `-sistors :165is connectedacross the junctionsfbetweenre- ,sistor l160 and capacitor Y161, and resistor `161axandcapacitor 164,-the voltage across resistor165 istrepresented by the vector E,3, the difference between vectors Beland f-Ecz. Since the Vcurrentllowing through;resistor :165 also ows @through 4capacitor 161, :a voltage appears r.across -capacitor llduetothis `current-and.this voltage-is .rep- .zresentedgby'vector Eea andis perpendicular to .the vector -Em :Since the output of .thefintegr-atingicircuitis taken 'across .the -capacitorjEcb the output Fvoltage is reprefsentedzby the vector Eo ,which is .the `sum of vectors -Ec1':andffEc3. It is notedfthat, while the vvector Ecl can zneverrbe atright angles (90phase shift).to'the vector Ein, .the Vadditiomoi =,tl1e vector E cato Y`vector Ecl .makes it readily possible to obtainanf'output voltage :E0-having a 90 zphase :relation .to the input voltage Ein. This phase relation may be varied .slightly by varying the lrheostat `1.1.62. lAssumingthe voltage applied tothe integratingrnetwork Y.to bea1sine wave, then the integral -of the voltage input: is` a :cosine curve, and'the y90" l,phase :shifter herein disclosed integrates the output lof the cathode-followertube 151. This;integrator.has the adzvantage ithatthe phase angleof theoutput varies much less :as Va ffunctionfo'f frequency `than in the caseof the :conventional 'series :resistancefcapacitance phase shifter.

v."lhe ioutput o'f :the H coil `13 is connected to .the input of the .integrator -rcircuit 41 fby -way of `test-calibrate switch 552C, izero-operate switch .200 and the v:contacts 1120.1 yof :balance detector Vzrelay 202 .in balance Vdetector 203 l(to be described :in fmore detail later). Y'When Ithe zero-operate fswitch200^issin zero position, -the input .ofthe integrator .is grounded, so that any spurious voltage output of :the ,H Aamplifier may be vcompensated for during..calibrationrofithe system.

Typical .values :of `the components 'of :the integrator 'circuit lfor :operation :with input v4voltages having Ya pri- :mary frequency lof 60 :cycles :may :be as :follows: :Tube *.151 vis :a V1-2A'17., Iamplifier .tubes 170.-'and :1778 are16AU6.s, -fcapacitors 150, 161, i164 .rand 3184 are Y0.1 .mfd., :resistors 152:and 186.are l megohm, .resistor :153.is 449.00 ohms, yresistor '154 is 100,000 ohms, resistor :155 .is .200,000 rohms, capacitors 156 vand 181 are 30 mfd., capacitor '157 lis '.1 mfd., resistors 160,165, S2172 andySS J.are '500,000 ohms, rheostat l1l62.is.`5.0,000rohms,.resistor 163 iis 175,000 ohms, resistor 171 `is 2 megohms, resistor Y173 is '-222 lmegohms,fcapacitors 2174 and l188 Vare.20 fmfd. :resistor 11575 is 2000 fohms, 'potentiometer 176 .is 1000 ohms, capacitorI1-7f7-is v0.0l-mfd., resistor .1-'79fis 250,000 fohms, :resistor 'lt/80- is 8205000 ohms, resistor 182 vis l800 cohms, capacitor 183is 100 mfd. -andvresistor186 is49,000 i'ohms.' 'The vvplate of the lamp'lier itube 1178 is :coupled bycoup'ling capacitorl100tolthefgridiof'the rst amplier `tube `101fof the "H" amplifier.

The .aba-larice rde'tector ta large` connection mustbe` made on thearrn-34 ofqJotentiometer 18 in ordertoattain the .desiredY-iuxcdensity fin thelamination. Thisresults inv large momentarysig- .-nals being applied 'to the wattmeter 40l coils until 4the servomotor 33-'has1-stopped operating. Such large voltages mayu damagev the y. sensitive y:light-beam movement in the wattmeter. Inordertozprevent such damage, abal- `ance detector circuitf203v (Fig. 351)' disengages movement of the wattmeter when the servo system is carrying the arm-ofpotentiometer 34. Thelbalance detector is com prised of a transformer V204.havingaprimary winding Yconnectedto the inputleadsof'the.-servomotor 33y and-Fa .secondary.windngconnected to-a.120 cycle lterf205. .Theoutput of the filter I205A is. connected across vagpotentiometer 206,.and-the output from the-arm of thepotentiometer is connecte'dfto the.grid of ia vgas tetrode 207. Therplate of thefgas tetrodeis.connected to 'oneof the :alternating-current supply linese50bywayfof a-balance relay coil 202, andthe cathode .of theA gas tube is .'con- :nected ,to I.the other of the supply 'lines S50. The balance detector is connectedsuchthat, whena voltageappears -atfthe .output terminalsf of thefservo ampliier 32, th'efgas -tube is non-conductive due to x-a-.bias voltage appearing .across potentiometer .206, andthe contacts 208 of the balancerelay 202 fground the -i'nput lto f theintegrator circuit 41 (Fig. 3b), thereby preventing movement on the wattmeter. 7When 'no voltage :appears .at the output of the servo amplifier 32, the gas tube 207 is conductive :esincelthebiasidue'tovoltagejacross potentiometer 206 is removed, andthecontactsi201'ofbalancerelay 202 connect the input ito'thexintegratorto 'the`Hcoil 13 by way of .zero-operate" :switch `i520.

`thickness measuredautoma'tically interms of more readily determined "factors, 'and also to have the thickness factor automatically controlled in 'the system. `The average thickness of a lamination'ise'qual to:

where 4Wis thejwei'ghtof thelamination in pounds, `Wh

is theV weight'ofany material removed from the laminajtion inpounds, Vd is lthe density oflthe laminationand is va constant, VL islthelengthofthesheet and b is the width Vof the lamination. This equationfis readily solved bythe vthickness computer 'circuit '21?0 of`Fig. 3b. .In this circuit, one leg of a bridge circuit \211,is Vcomprised fa rheostat 212 whoseresistance^is"manually'adjusted to be directly proportional to the length L of the lamination, an adjacent leg lofthebridge is comprised of a rheostat 213 whose resistance'is manually adjusted to be inversely Vproportionalto 'the Width b 'ofthe lamination, the other adjacent leg of the bridge is comprised of a series comvbination of a rheostat `214whose resistance 'is manually adjusted to be proportional to 'the weight W of the lamination and a rheostat '215 whose resistance is manually adjusted to beproportional to the Vweig'ht'WI of material removed from 1holesdrilledin the lamination. The opposite leg of thebridge contains a fixed resistance 216 proportional to'the 'exp'ectedminimum thickness of a ls'heet of lamination material nominally l12 mils thick. Rheostat 217 in .series with resistor206 is proportional "to the'thickness -of one 's'heetoverthe range of'thickness `vto'be measured. "The resistorljinayfbe varied to'c'ompensate ffor variations in `l`the density o'f 'the 'sheetibeing tested.'V potential is applied across opposite corners of vthe bridge'by means of a suitable s ourceof voltageA 218,

andthe other corners'of the bridge are connectedY to the input of a servo amplifier 219. The servo amplilier is l connected to a servomotor 220 which controls the setting of the arm of potentiometer 217. When the rheostats 212, 213, 214 and 215 are manually set to values proportional respectively to the length, width, weight and hole weight of the lamination, the resistance of vvrheostat 217 is automatically adjusted to be proportional to theV thickness of the lamination when the bridge is balanced. A resistor 221 with non-linear taps in series with the input to servo amplifier 219 is mechanically also controls the resistance of rheostats 222 and 223 which are connected in the flux density computer circuit Vin place of thickness rheostat 22a and compensator 22b respectively when the switches 60a and 60b are in automatic position. The switch 56] of ganged range switch 56 replaces resistance 216 in the bridge circuit with resistance 224 to change the range of the computer from a nominal value of 12 mils to a nominal value of 14 mils.

The calibrator and calibration VIn order to check the accuracy of the loss tester, a calibrationstandard circuit 230 (Fig. 3a) is provided. This circuit is comprised of a series circuit of a capacitor 231, and three resistances 232, 233 and 234. When the test-calibrate switch 52 is in calibrate position, the capacitor 231 is connected to the width adjust rheostat 21 (Fig. 3B) `and the output of power amplier 19 (Fig. 3a), and the input of the integrator 41 (Fig. 3b) is connected to the junction of resistors 232 and 233 or `233 and 234 depending upon the position of range switch" 235. lThe other end of resistor 234 is grounded. This calibrator circuit simulates a hypotential lamination of known characteristics, such as power loss per pound, width, thickness and power factor.

' In order to calibrate the instrument, the width rheostat 21, thickness rheostat 22a and compensator 22b,

Weight rheostat 214, hole weight rheostat 215, and length rheostat 212 are set to values correspondingY to a hypotential lamination, having a known loss characteristic, the automatic-manual thickness switch 60 is set to manual position, the test-calibrate switch 52 is set to calibrate, the calibrator range Vswitch 235 is set to the same range as the range switch 56, and the operatezero switch 200 is set to the zero position.

. YThe first step of the calibration consists of setting the mechanical zero of the wattmeter by conventional means ,(not shown). This adjustment compensates for spurious voltages arising in the integrator 41 and H amplifier-42. Then, with the operate-zero switch 200 returned to operate position, and a voltmeter (not shown) connected to-terminals 71 in the ux density computer cirlcuitj55, the volts potentiometer 25 is adjusted until a predetermined voltage corresponding to the desired ux density in the hypotential. sample is indicated on the voltmetcr. Y f y Y Y .Y

, Ifdcsired the volts potentiometer 35 may be calibrated so that power loss readings may be obtained for `a number of different liux densities in the sheet.A

' A predetermined portion of the voltage indicated by 'the voltmeter appears at the input to the integrator due 'to vthe action'of the calibrator 230. In the next step of calibration, theY watts potentiometer 24 is adjusted, thereby.t adjustingrthe input voltage to the B amplilier, funtila predetermined loss is indicated by the wattmeter 40.` When the .fmanual-automatic thickness switch is Aturned tofthe automatic position, the volts indicated Yon the`voltmeter'and the loss indicated on the watt- I2 vmetei should not change. A YSimilar procedure is followed for calibration of the other range. While this invention has been disclosed with particular reference to determining the losses of single sheets of magnetic material, it may also be adapted as a continuously measuring quality control apparatus for use on continuously moving sheets. In thisA case the thickness factor may be automatically applied to the computer by means of thickness measuring apparatus such as X-ray gauges, beta gauges, or mechanical gauges. Similarly, the width factor may also be automatically applied to the computer, so that no manual adjustment is necessary. Although the results of this test are not necessarily related to the loss in the cut -laminations, it does give an indication of the quality of the sheet. v

In a modiiicatiou of the circuit of this invention, a cathode follower may be employed to isolate the computer from the B coil so that no current is drawn through the B coil. indications of power loss, since a small amount of error does arise from allowing current to flow through the B coil.

It will be understood, of course, that, while the form of the invention herein shown and described constitutes a preferred embodiment of the invention, it is not 1ntended herein to illustrate all of the possible equivalent forms or ramifications thereof. It will also be understood that the words used are words of description rather than of limitation, and that various changes may be made without departing from the spirit or scope of the invention herein disclosed, and it is aimed in the appended claims to cover all such changes as fall within the true spirit and scope of the invention.

' What we claim as new and desire to secure by Letters Patent of the United States is:

l. In an apparatus for determining the power losses of a sheet of `magnetic material, means inducing a predetermined flux in said sheet, rst inductive means surrounding said sheet providing a rst voltage output proportional to the ilux in said sheet, second inductive means adjacent said sheet providing a second voltage output proportional to the tlux in the eld adjacent said sheet, means integrating said second voltage and means actuated by said iirst voltage vand said integrated second voltage for indicating said energy losses.

2. In an apparatus for determining the power losses of a sheet of magnetic material, tirst inductive means surrounding said sheet for inducing therein a predetermined flux, second inductive means surrounding said sheet internal to said rst inductive means and providing a first voltage output proportional to the flux in said sheet, third inductive means adjacent to said sheet internal to said rst inductive means providing a second voltage output proportional to the llux in the lield adjacent said sheet, means integrating said second voltage, a wattmeter having lirst and second windingsand means connecting said first voltage to said rst winding and said integrated second voltage to said second winding.

3. In an apparatus for determining the power losses per unit weight of a sheet of magnetic material, means inducing a predetermined constant flux density in said sheet, means providing a first voltage output proportional to said flux density, means providing a second voltage proportional to the elective current magnetizing said sheet, and means actuated by said lirst voltage and said second voltage for indicating said losses.

4.V In an apparatus for determining the power losses per unit weight of a sheet of magnetic material, means inducing a predetermined constant flux density in said sheet, means providing a tirst voltage output proportional to said ux density, inductive means adjacent said lamination providing a second voltage proportional to the flux in the tield adjacent said lamination, means integrating said second voltage, and means actuated by s aid rst voltage and said second voltage for indicating said losses.

This may result in more accurate amena/t1 d3 5. .In an Aapparatus,for :determining Lthe 'power losses per unit weight of a sheet of magnetic materialirstginduct-ive means for inducinga, flux i. n,said,sheet andiA providing .a first voltage: proportionalto the-magnetizing ,force appliedtosaid sheet, vva variable .voltage=.sonroe forenergizing said,first inductivemeans, second inductive mea-ns providing a second .voltage :proportional tothe fluxin said sheet, computerl means ,connected tot saidrsecond voltage providing" a .third zvoltage lproportional .to `the flux density in Ysaid sheet, servo meansconnectedto, saidcomputer means for maintaining constant Alux density lin said lamination by controlling said `variable voltage source, and means connecting said first and third voltages to a Wattmeter.

6. In an apparatus for `determining the power losses per unit weight of asheetlof magnetic material, first coil means surrounding said sheet forinducing a -fuxiinsaid sheet, a variable voltage source for energizing .said rst coil means, a second coil means surrounding said sheet insideof said first coil means providing a rstwoltage ,output proportional tothe fluxjn said,sheet,c on iputer means connected'to said second coil means providing a second voltage proportional to the flux density in said sheet, servo means connected to said computer means for maintaining a predetermined constant flux density in said lamination by controlling said variable voltage source means providing a third voltage proportional to the current energizing said sheet, and means connecting said second and third voltages to a wattmeter.

7. In an apparatus for determining the power losses per unit weight of a sheetV of magnetic material, first coil means surrounding said sheet for inducing a flux in said sheet, a variable voltage source for energizing -said first coil means, a second coil means surrounding said sheet inside of said first coil means providing a first voltage output proportional to the flux in said sheet, flux density computer means connected in series with said second coil means, and providing second and third voltage outputs proportional to the flux density, in said sheet, servo means actuated by said second voltage output for maintaining a predetermined constant flux density in said lamination and maintaining said third voltage proportional to said flux density by controlling said variable voltage source, means providing a fourth voltage proportional to the current energizing said sheet, and means connecting said third and fourth voltages to a wattmeter.

8. In an apparatus for determining the power losses per unit weight of a sheet of magnetic material, first coil means surrounding said sheet for inducing a ux in said sheet, a variable voltage source for energizing said first coil means, a second coil means surrounding said sheet inside of said first coil means providing a first voltage output proportional to the flux in said sheet, flux density computer means connected in series with said second coil means and providing a second and third voltage outputs each proportional to the flux density in said sheet, servo means actuated by said second voltage output for maintaining a predetermined constant flux density in said sheet and maintaining said third voltage proportional to said flux density by controlling said variable voltage source, third coil means adjacent said sheet inside of said first coil means for providing a fourth voltage output proportional to the flux in the field adjacent said sheet, means integrating said fourth voltage, and means connecting said third voltage and said integrated fourth Voltage to a wattmeter.

9. ln an apparatus for determining the power losses per unit weight of a sheet of magnetic material, first coil means surrounding said sheet for inducing a ux in said sheet, a variable voltage source for energizing said first coil means, a second coil means surrounding said sheet inside of said first coil means providing a first voltage output proportional to the flux in said sheet, uX density computer means connected in series with said second coil means, said computer means comprising a first potentiometer means connectedv in series with a .second Avpotentiometer means, .variable `resistance ,means connected to said secondcoil means and in, series with-said Apotentiometer means andfhaving avoltagedrop proportional to-the area of-,said sheet, servovmeans connectedto the arm. ofsaid rstpotentiometer, means for; maintaining aypredetermined constanttfluxdensity in said;sheet ,by controlling .said variable voltage .source,ithe,arm of,said second potentiometer providing a second f potential ,I proportional `to saidiiux density, I.means providingathird voltage proportional tothe current, energizing said sheet, 2a wattmeter, ,and` amplifying :means connecting saidl second ,and lthird .voltages tok said Wat-tmeter.

10. ,In an apparatus for determining the `powerllosses per unit weightiof a -sheetoftmagnetic material,;frst coil .means .surrounding said sheetforinducingafux in` said jsheetfa variable 4Voltage-.sourcefor energizingsaid first coil ,means, a secondcoil means surrounding fsaid` sheet vkinside of saidrst coil means providing a,rst voltage ,output proportional vto f the -flux in. said sheet, .uxdensity computer means connected inseries ,with said ,second coil means, said computer means comprising a first potentiometer means connected in series with a second potentiometer means, variable resistance means connected to said second coil means in series with said potentiometers and having a voltage drop proportional to the area of said sheet, servo means connected to the arm of said first potentiometer means for maintaining a predetermined constant iiux density in said sheet by controlling said variable voltage source, the armof said second potentiometer providing a second potential proportional to said flux density, third coil means adjacent said sheet inside of said first coil means providing a third voltage proportional to the flux in the field adjacent said sheet, means integrating said third voltage, a wattmeter, and amplifying means connecting said second voltage and said integrated third voltage to said wattmeter.

11. In an apparatus for determining the power loss per unit weight of a sheet of magnetic material, first coil means surrounding said sheet for inducing a flux in said sheet, a variable voltage source energizing said first coil means, a second coil means surrounding said sheet inside of said first coil means and providing a first voltage output proportional to the flux in said sheet, fiuX density computer means connected in series with said second coil means, said computer comprising a first potentiometer having a resistance proportional to the width of said sheet, a second potentiometer having a resistance proportional to the thickness of said sheet, said second potentiometer being in series with third and fourth potentiometers having arms, said second, third and fourth potentiometers being in series with said first potentiometer and in parallel with a fifth potentiometer to form a parallel circuit, said fifth potentiometer being mechanically coupled to said second potentiometer so that variations made on said second potentiometer do not vary the resistance of said parallel circuit, the circuit values of said computer circuit being selected so that the second and third voltages at the arm of said third and fourth potentiometers respectively are proportional to the flux density of said sheet, servo means connected to the arm of said fourth potentiometer and coupled to said variable voltage source to maintain said flux density constant, means providing a fourth voltage proportional to tne current magnetizing said sheet, a wattmeter, and means connecting said second and fourth voltages to said wattmeter.

12. In an apparatus for determining the power loss per unit weight of a sheet of magnetic material, first coil means surrounding said sheet for inducing a flux in said sheet, a variable Voltage source energizing said rst coil means, a second coil means surrounding said sheet inside of said first coil means and providing a first voltage output proportional to the flux in said sheet, flux density computer means connected in series with said second coil means, said computer comprising a first potentiometer circuit, said fifth potentiometer being mechanically cou-v pled to said second potentiometer so that variations made on said second potentiometer do not` vary the resistance of said parallel circuit, the circuit values of said computer circuit being selected so that the second and third voltages at the arm of said third and fourth potentiometers respectively are proportional to the ux density of said sheet, servo means connected to the arm of said fourth potentiometer and coupled to said variable voltage source to maintain said flux density constant, third coil means adjacent said sheet inside of said irst and second coils and providing a fourth voltage proportional to the ux in the lield adjacent said sheet, means integrating said fourth voltage, a wattmeter, and means connecting 16 said second and integrated fourth voltages to said Wattmeter.

13. In an apparatus for determining the power losses per unit weight of a sheet of magnetic material, means inducing a predetermined constant flux density in said sheet, means providing a first voltage output proportional to said flux density, means including core means disposed in a magnetic eld adjacent said sheet and not encircling said sheet providing a second voltage proportional to the elective current magnetizing said sheet, and means actuated by said rst voltage and said second voltage for indieating said losses.

References Cited in the le of this patent UNITED STATES PATENTS 

